An antenna is an electrical device that converts electric power into radio waves, and/or vice versa. Antennas are usually used with, or provided as part of, a radio transmitter and/or radio receiver. They are used in systems such as radio broadcasting, television, radar, cell phones, satellite communications, etc. The polarization of an antenna refers to an orientation of an electric field of a radio wave with respect to the Earth's surface and is determined by the physical structure of the antenna and by its orientation, which is different from the antenna's directionality.
By convention, an antenna's polarization is understood to refer to the direction of the electric field. Two special cases are linear polarization and circular polarization. In linear polarization, the electric field of the radio wave oscillates back and forth along one direction. This can be affected by the mounting of the antenna, but usually the desired direction is either horizontal or vertical polarization. In circular polarization, the electric field and magnetic field of the radio wave rotates at the radio frequency circularly around the axis of propagation.
Although linear polarized antennas have a far-field electric-field vector that is confined to a plane along the electromagnetic wave propagation direction, the far-field electric-field vector of a circularly polarized antenna has a constant magnitude and changes in a rotary manner along the propagation direction. Therefore, circularly polarized antennas can reduce the loss caused by a misalignment between the transmitter and receiver antennas, and suppress multipath effects caused by buildings and the ground.
The above-described background relating to antennas for various wireless applications is merely intended to provide a contextual overview of antenna technology, and is not intended to be exhaustive. Other context regarding antennas may become further apparent upon review of the following detailed description.